Image reading apparatus and image forming apparatus equipped therewith

ABSTRACT

An image reading apparatus has a light source unit for illuminating an object to be illuminated, a reading unit for reading the object illuminated by the light source unit, a reflective unit, having at least a first reflection mirror, for reflecting reading light reflected by the object toward the reading unit, and a first light blocking portion for partially blocking light except the reading light. The first reflection mirror has a reflecting surface for reflecting the reading light, and an end surface substantially orthogonal to the reflecting surface. The first light blocking portion extends in a longitudinal direction of the first reflection mirror toward the end surface of the first reflection mirror, with a tip end of the first light blocking portion being opposed to the end surface of the first reflection mirror with a gap therebetween.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(a) to PatentApplication No. 2014-123630, filed in Japan on Jun. 16, 2014, the entirecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an image reading apparatus for readingan original, etc., and an image forming apparatus equipped with thisimage reading apparatus.

Related Art

In this type of image reading apparatus, the reading operation isperformed while an original is transported in a sub-scanning directionon a glass, by allowing a light source unit below the glass toilluminate the original and allowing an imaging element such as a CCD(Charge Coupled Device) to scan the original repeatedly in a mainscanning direction. The reading operation is also performed while anoriginal is positioned and set on a glass, by allowing the light sourceunit, the imaging element, etc. below the glass to move in asub-scanning direction, allowing a light source unit to illuminate theoriginal, and allowing the imaging element to scan the originalrepeatedly in a main scanning direction. The light source unit forilluminating the original may be of various types, including afluorescent light or an LED array.

According to the image taking process by this image reading apparatus,the light for illuminating the original is emitted by the light sourceor the like and reaches an original surface via the light guiding memberor the like. The reflected light (reading light) that is reflected bythe original surface is guided along a predetermined optical path to theimaging element such as a CCD. In this process, light which reaches theimaging element from an unintended optical path (so-called stray light)causes adverse influences such as noise or ghost in the taken image ofthe original.

Attempts to reduce such adverse influences by stray light have been madeand known in the conventional art. JP 2013-138388 A (hereinafter called“Patent Literature 1”) prevents stray light by placing a light blockingplate in the vicinity of a light guiding member which is arrangedclosely to the light source. If the angle of emission by the lightguiding member deviates from the regular range, the light blocking plateprevents such light from entering a reflection mirror. JP 2004-157174 A(hereinafter called “Patent Literature 2”) provides an elastic lightblocking member between a light source and a contact glass on which anoriginal is set. An original is illuminated with light through aslit-like opening formed in the main scanning direction. Then, readinglight reflected by the original is allowed to be incident on a mirrorfrom the slit-like opening and is led to the imaging element.

However, stray light to be blocked by Patent Literature 1 is limited tothe one which is directly incident on the mirror through the lightguiding plate on the light source side. When light is reflected by theoriginal and incident on the mirror (as reflected light, or readinglight), it is impossible to prevent a portion of the reflected lighttravelling along an unintended optical path (as stray light) fromreaching the imaging element. Hence, Patent Literature 1 fails toprovide sufficient measures against stray light.

In Patent Literature 2, a frame for holding the light source is incontact with the mirror and covers a part of the reflecting surface ofthe mirror. This structure decreases an area of the mirror on which thereading light is incident. Hence, there are risks of vignetting of thereading light, or deviation of an optical axis of the mirror due tothermal deformation of the frame under the operational heat. Besides, ifthe mirror and the frame are separated in Patent Literature 2 in orderto prevent such vignetting and deviation of the optical axis, it isdifficult to block stray light which passes through a gap between themirror and the frame. In this case, incident light on a side surface ofthe mirror, which is not the reflecting surface, may also act as straylight.

For a carriage structure in which the light source unit and the readingunit are integrated, it is particularly difficult to provide sufficientmeasures against stray light. This is because, in comparison with astructure in which the light source unit and the reading unit areseparated from each other, the carriage structure has a smaller distancefrom the slit through which the reading light from the original entersto the CCD serving as the imaging element. It is also because thecarriage structure requires a complicated arrangement for the reflectiveoptical system and the optical path in order to reflect the readinglight to the imaging element.

SUMMARY OF THE INVENTION

The present invention provides an image reading apparatus and an imageforming apparatus which are capable of preventing stray lighteffectively, while preventing not only deviation of an optical axis dueto interference between the frame and the mirror but also vignetting ofthe reading light on the reflecting surface side of the mirror.

An image reading apparatus according to the present invention includes:a light source unit for illuminating an object to be illuminated; areading unit for reading the object illuminated by the light sourceunit; a reflective unit, having at least a first reflection mirror, forreflecting reading light reflected by the object toward the readingunit; and a first light blocking portion for partially blocking lightexcept the reading light. The first reflection mirror has a reflectingsurface for reflecting the reading light, and an end surfacesubstantially orthogonal to the reflecting surface. The first lightblocking portion extends in a longitudinal direction of the firstreflection mirror toward the end surface of the first reflection mirror,with a tip end of the first light blocking portion being opposed to theend surface of the first reflection mirror with a gap therebetween.

In this image reading apparatus of the present invention, the endsurface of the first reflection mirror is opposed to the first lightblocking portion. This structure can prevent vignetting of the readinglight on the reflecting surface side and can simultaneously prevententry of stray light at the end surface of the first reflection mirror.In addition, the gap between the end surface and the first lightblocking portion avoids interference between the first reflection mirrorand the first light blocking portion. Therefore, even when the frame isdeformed due to impact or heat, this structure can limit deformation orfall of the first reflection mirror and can prevent deviation of theoptical axis of the first reflection mirror.

The image reading apparatus of the present invention may be alsoequipped with a scanner for scanning the object (the object to beilluminated), the scanner having a housing and a lid-like holding memberprovided with respect to the housing. The light source unit may be heldby the lid-like holding member. The first light blocking portion may beintegrally molded with the lid-like holding member.

Integral molding of the first light blocking portion with the lid-likeholding member enables a simple and high-precision positioning of thefirst reflection mirror and the first light blocking portion, and canfurther improve the mechanical strength of the lid-like holding member.Since the first light blocking portion can be molded in the same step asthe molding of the lid-like holding member, it is also possible tosimplify the production process and to reduce the number of components.

In the image reading apparatus of the present invention, reflected lightfrom the object (the object to be illuminated) may be firstly reflectedby the first reflection mirror.

In this case, the first light blocking portion is provided face to facewith the end surface of the first reflection mirror which is arrangedmost closely to an original, which is an object to be illuminated. As aresult, stray light from the outside can be blocked effectively.

The image reading apparatus of the present invention may be alsoequipped with another reflection mirror fixed in the housing, and asecond light blocking portion, provided between the gap and a reflectingsurface of the other reflection mirror, for blocking stray light thathas passed through the gap.

The thus provided second light blocking portion can block the straylight which has passed through the gap between the end surface of thefirst reflection mirror and the first light blocking portion, and canprevent the stray light further.

In the image reading apparatus of the present invention, the lightsource unit may be equipped with an elongated light guiding memberhaving translucency, and a light emitting element provided on alongitudinal end side of the light guiding member.

This arrangement not only achieves miniaturization of the light sourceunit but also allows light to be evenly illuminated on the original.

Additionally, an image forming apparatus according to the presentinvention includes the image reading apparatus according to the presentinvention as described above, and a printing unit for printing an imageof the object (the object to be illuminated) on a recording sheet, theimage being read by the image reading apparatus.

This image forming apparatus can achieve similar operations and effectsto those achieved by the above-mentioned image reading apparatus of thepresent invention.

In the present invention, the end surface of the first reflection mirroris opposed to the first light blocking portion with a gap. Thisstructure can prevent vignetting of the reading light on the reflectingsurface side and can simultaneously prevent entry of the stray light atthe end surface of the first reflection mirror. Besides, even when theframe is deformed due to impact or heat on the apparatus, this structurecan limit deformation or fall of the first reflection mirror and canprevent deviation of the optical axis of the first reflection mirror.Accordingly, it is possible to provide an image reading apparatus and animage forming apparatus which are capable of preventing stray lightsufficiently, while preventing not only deviation of the optical axisdue to interference between the frame and the mirror but also vignettingof the reading light on the reflecting surface side of the mirror.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of an image forming apparatus equipped with animage reading apparatus according to the first embodiment of the presentinvention.

FIG. 2 is a cross section of an image reading apparatus and an originaltransporting apparatus in FIG. 1.

FIG. 3 is an enlarged cross section of a scanning unit.

FIG. 4 is an enlarged partial cross section of the scanning unit,showing reading light and stray light inside the scanning unit.

FIG. 5 is a perspective view of the scanning unit.

FIG. 6 is an enlarged perspective view of an end of the scanning unit.

FIG. 7 is an enlarged cross section of a scanning unit according to thesecond embodiment.

FIG. 8 is an enlarged partial cross section of the scanning unitaccording to the second embodiment, showing reading light and straylight inside the scanning unit.

DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment

Embodiments of the present invention are hereinafter described withreference to the drawings.

FIG. 1 is a cross section of an image forming apparatus equipped with animage reading apparatus according to the first embodiment of the presentinvention. The image forming apparatus 1 has a copier function ofreading an original and printing an image on a recording sheet, and isequipped with an image reading apparatus 2, an original transportingapparatus 3, a printing unit 4, a feeding cassette 5, etc.

Image data processed by this image forming apparatus 1 are color imagedata composed of black (K), cyan (C), magenta (M), and yellow (Y), andmonochrome image data composed of one color (e.g. black). To form fourkinds of toner images corresponding to these colors, the printing unit 4include four development devices 12, four photosensitive drums 13, fourdrum cleaning devices 14, and four charging units 15, which constitutefour imaging stations Pa, Pb, Pc, Pd corresponding to black, cyan,magenta, and yellow, respectively.

In each of the imaging stations Pa, Pb, Pc, Pd, residual toner on thesurface of the photosensitive drum 13 is removed and collected by thedrum cleaning device 14. Then, the surface of the photosensitive drum 13is evenly electrostatically charged at a predetermined potential by thecharging unit 15. The surface of the photosensitive drum 13 is exposedby the optical scanning device 11 to form an electrostatic latent imageon the surface. An electrostatic latent image formed on the surface ofthe photosensitive drum 13 is developed by the development device 12 toform a toner image on the surface of the photosensitive drum 13. In thismanner, a toner image of each color is formed on the surface of thephotosensitive drum 13.

Subsequently, while an intermediate transfer belt 21 revolves in thedirection of arrow C, residual toner on the intermediate transfer belt21 is removed and collected by a belt cleaning device 25. Thereafter,the toner image of each color formed on the surface of thephotosensitive drum 13 is sequentially transferred on top of each otherto form a color toner image on the intermediate transfer belt 21.

A nip region is formed between the intermediate transfer belt 21 and atransfer roller 26 a of a secondary transfer device 26. While arecording sheet transported in a sheet transport path R1 passes throughthe nip region in a sandwiched manner, the color toner image formed onthe surface of the intermediate transfer belt 21 is transferred on therecording sheet. The recording sheet is then heated and pressed betweena heating roller 31 and a pressure roller 32 of a fixing device 17, sothat the color toner image on the recording sheet is fixed.

Incidentally, a recording sheet is picked up from the feeding cassette 5by pick-up rollers 33, conveyed in the sheet transport path R1 via thesecondary transfer device 26 and the fixing device 17, and discharged toa discharge tray 39 through discharge rollers 36. The sheet transportpath R1 is provided with registration rollers 34, transport rollers 35,the discharge rollers 36, and the like. The registration rollers 34 stopthe recording sheet temporarily to align the leading end of therecording sheet, and resumes transport of the recording sheet insynchronization with the transfer timing of the color toner image at thenip region between the intermediate transfer belt 21 and the transferroller 26 a. The transport rollers 35 promote transport of a recordingsheet.

In the case where an image is printed not only on the front side of therecording sheet but also on a reverse side thereof, the recording sheetis transported in reverse from the discharge rollers 36 to a reversepath Rr where the recording sheet is turned over. The inverted recordingsheet is guided again to the registration rollers 34, so that an imageis recorded and fixed on the reverse side of the recording sheet in asimilar manner as the front side of the recording sheet. Finally, therecording sheet is discharged to the discharge tray 39.

Next, the description turns to the image reading apparatus 2 accordingto the first embodiment. FIG. 2 is a cross section of the image readingapparatus 2 and the original transporting apparatus 3.

In FIG. 2, the far side of the original transporting apparatus 3 ispivotally hinged with one side of the image reading apparatus 2 which islocated below (a hinge is not shown). The original transportingapparatus 3 is opened and closed by raising and lowering the near sideof the original transporting apparatus 3. When the original transportingapparatus 3 is opened, a platen glass 41 of the image reading apparatus2 becomes accessible.

The image reading apparatus 2 is equipped with a platen glass 41, anoriginal reading glass 42, a scanning unit 43, a movement unit 44, etc.The movement unit 44 includes a guide shaft 48 for guiding the scanningunit 43 in the sub-scanning direction Y, and a driving unit (not shown)for moving and positioning the scanning unit 43 in the sub-scanningdirection Y.

The scanning unit 43 includes a light source unit, an imaging lens 46, aCCD (Charge Coupled Device) 47, first to fifth reflection mirrors 51-55which constitute a reflection unit, etc. The scanning unit 43 is movedby the movement unit 44 to a position below the platen glass 41 or theoriginal reading glass 42, so as to read an original (an object to beilluminated) set on the platen glass 41 (first reading mode) or to readan original (an object to be illuminated) conveyed over the originalreading glass 42 (second reading mode).

In the first reading mode, the scanning unit 43 is moved by the movementunit 44 to a position below the platen glass 41. The originaltransporting apparatus 3 is opened in order to set an original on theplaten glass 41, and then closed. While the scanning unit 43 is moved bythe movement unit 44 at a fixed speed in the sub-scanning direction Y,by a distance corresponding to the size of the original, the original onthe platen glass 41 is illuminated by the light source unit. Lightreflected by the original is sequentially reflected by the first tofifth reflection mirrors 51-55 and guided to the imaging lens 46, alongthe optical path shown in dashed line in the figure. The imaging lens 46focuses the light reflected by the original on the CCD 47 and allows animage on the front side of the original to be formed on the CCD 47(reading unit). The CCD 47 repeatedly scans the image on the front sideof the original in the main scanning direction X and thereby reads theimage on the front side of the original.

In the second reading mode, the scanning unit 43 is moved and positionedby the movement unit 44 to a position below the original reading glass42. The original transporting apparatus 3 draws out an original from anoriginal tray 56, conveys the original in the sub-scanning direction Yover the original reading glass 42, and discharges the original to theoriginal discharge tray 57. While the original passes over the originalreading glass 42, the front side of the original is illuminated throughthe original reading glass 42 by the light source unit in the scanningunit 43. Light reflected by the front side of the original issequentially reflected by the first to fifth reflection mirrors 51-55 inthe scanning unit 43 and guided to the imaging lens 46, along theoptical path shown in dashed line in the figure. The imaging lens 46focuses the light reflected by the front side of the original on the CCD47 and allows an image on the front side of the original to be formed onthe CCD 47. The CCD 47 repeatedly scans the image on the front side ofthe original in the main scanning direction X and thereby reads theimage on the front side of the original.

Regarding the light source unit in the scanning unit 43, light guidingmembers 71 are arranged on both sides of a slit St which extends in themain scanning direction X. In each of the light guiding member 71, LEDs72 (light emitting elements, see FIG. 4) are provided on light incidentplanes at both ends of the light guiding member 71. Instead of LEDs 72,other types of semiconductor devices, light bulbs, etc. are alsoapplicable.

Each light guiding member 71 is composed of an elongated translucentmain body having translucency and having a substantially cylindricalshape. The light guiding member 71 has light incident planes on thelongitudinal ends of the translucent main body. A light exit plane 71 ais formed on a longitudinal side surface of the translucent main body. Alight reflecting plane is formed on another longitudinal side surface ofthe translucent main body, opposite to the light exit plane. The lightguiding members 71 are made by shaping an acrylic resin in a mold.

According to the light source unit having this configuration, the LEDs72 are arranged face to face with the light incident planes at both endsof each light guiding member 71. Hence, light emitted from the LEDs 72is incident on the light incident planes of the light guiding member 71,guided inside the light guiding member 71, and exits directly from thelight exit plane or exits from the light exit plane after reflected bythe light reflecting plane.

The light exit plane of each light guiding member 71 is oriented to thesame position of an original, with the interposition of the platen glass41 or the original reading glass 42. The light emitted from the lightexit planes of the light guiding members 71 is incident on the sameposition of an original to illuminate this particular position of theoriginal. The light reflected at the particular position of the originalis guided as reading light through the slit St into the scanning unit43. The reading light is sequentially reflected by the first to fifthreflection mirrors 51-55, and enters the CCD 47 through the imaging lens46. Then, the CCD 47 reads an image on the front side of the original.

Now, the configuration of the scanning unit 43 and the light source unitis described in greater detail. FIG. 3 is a cross section of thescanning unit 43. FIG. 4 is an enlarged partial cross section in thevicinity of the light blocking member in the light source unit. FIG. 5is a perspective view of the scanning unit 43. FIG. 6 is an enlargedperspective view of an end of the scanning unit 43.

As shown in FIG. 3 to FIG. 6, the scanning unit 43 has an open-tophousing 61, a lid-like holding member 62 which can open and close theopening at the top of the housing 61, a light source unit provided onthe lid-like holding member 62, and a CCD board 63 provided on alongitudinal side wall of the housing 61 (a side wall which extendslongitudinally, namely, in the main scanning direction X).

The housing 61 accommodates the imaging lens 46 and the first to fifthreflection mirrors 51-55. The lid-like holding member 62 substantiallycovers the opening at the top of the housing 61, and holds the lightsource unit. The CCD board 63 mounts the CCD 47, with thelight-receiving surface of the CCD 47 facing the inside of the housing61 through a slit (not shown) formed in the side wall of the housing 61.

The lid-like holding member 62 is provided with two engagement grooves62 a extending in the main scanning direction X and a slit St betweenthe engagement grooves 62 a. Each of the engagement grooves 62 areceives the substantially columnar light guiding member 71.Accordingly, the shape of the engagement grooves 62 a corresponds to apart of the columnar side face. The light source unit allows the lightfrom the LEDs 72 to be incident on the light incident planes at bothends of each light guiding member 71, to exit from the light exit planeat one side surface of the light guiding member 71, and to illuminate anoriginal through the platen glass 41 or the original reading glass 42.The reading light reflected by the original is transmitted through theplaten glass 41 or the original reading glass 42, guided into thehousing 61 through the slit St in the lid-like holding member 62,sequentially reflected by the first to fifth reflection mirrors 51-55,and finally enters the CCD 47 through the imaging lens 46.

In addition to the two light guiding members 71 and four LEDs 72, thelight source unit is equipped with two LED boards 64 each mounting twoLEDs 72, and two radiator plates overlaid on the outer surface of eachLED board 64.

The light guiding members 71 are fitted in and held by the engagementgrooves 62 a at shielding parts 62 b, 62 c of the lid-like holdingmember 62, with both ends of each light guiding member 71 extending tothe connecting parts on both sides of the lid-like holding member 62.The light incident planes of the two light guiding members 71 arepositioned at opening apertures in the connecting parts. The LED boards64 and the radiator plates are attached to the connecting parts. TheLEDs 72 on the LED boards 64 are positioned at the opening apertures inthe connecting parts. Namely, both ends of the two light guiding members71, the LEDs 72, the two LED boards 64, and the two radiator plates arelocated on the outside of the housing 61.

Each of the first to fifth reflection mirrors 51-55 is provided with areflective coat formed on one side of a piece of glass by silver vapordeposition, and has a reflecting surface on which the reflective coat isformed, end surfaces substantially orthogonal to the reflecting surface,and a back surface opposite to the reflecting surface. The crosssectional shape of these mirrors is generally rectangular, withchamfered corners. The first to fifth reflection mirrors 51-55 are fixedin the housing 61 by mirror holders (not shown), at predeterminedpositions and angles on the optical path of the reading light reflectedby the original. The first reflection mirror 51, located substantiallyjust under the slit St, is the first mirror on which the reading lightcoming through the slit St in the lid-like holding member 62 isincident.

As shown in FIG. 3 and FIG. 4, the light guiding members 71 are fittedin the engagement grooves 62 a in the lid-like holding member 62. One ofthe engagement grooves 62 a is integrated with a rib-shaped first lightblocking portion 81 a which extends longitudinally along the lightguiding member 71, on the back side of the groove exposed to the insideof the housing 61. The longitudinal length of the first light blockingportion 81 a is substantially equal to the longitudinal length of thefirst reflection mirror 51. The tip end of the rib-shaped first lightblocking portion 81 a is opposed to an end surface of the firstreflection mirror 51, with a gap therebetween. These components areopposed in the vicinity of a chamfered corner between the end surfaceand the reflecting surface. Thus, the tip end of the first lightblocking portion 81 a does not cover the reflecting surface of the firstreflection mirror 51, and does not contact with the first reflectionmirror 51.

Since the tip end of the first light blocking portion 81 a does notcover the reflecting surface of the first reflection mirror 51, thisstructure does not hamper entry of the reading light at the reflectingsurface of the first reflection mirror 51, and can prevent vignetting ofthe reading light. If stray light enters the end surface of the firstreflection mirror 51, the stray light that has entered from the endsurface is transmitted through the glass of the first reflection mirror51. As a result, stray light reflected or refracted inside the mirror isallowed to enter the inside of the housing 61. However, according to thepresent invention, the first light blocking portion 81 a is opposed tothe first reflection mirror 51 in the vicinity of the corner near thereflecting surface of the first reflection mirror 51, this structure canprevent the stray light 82 a which enters through the slit St from beingincident on the end surface of the first reflection mirror 51 and fromreaching the CCD 47 through the inside of the housing 61. Since thelength of the first reflection mirror 51 is substantially equal to thelength of the first light blocking portion 81 a, the above-mentionedmeasures against stray light can block stray light over the entirelength of the first reflection mirror 51 and can improve the effectfurther.

Besides, since the tip end of the first light blocking portion 81 a isseparated by a gap from, and is not in contact with, the end surface ofthe first reflection mirror 51, this structure addresses deformation ofthe frame and other accidents due to external impact or heat during theoperation or transport of the image forming apparatus and the imagereading apparatus. In case of such accidents, this structure can avoidinterference between the first reflection mirror 51 and the first lightblocking portion 81 a, and can reduce the risk of deviation of theoptical axis of the first reflection mirror 51 due to deformation orfall of the first reflection mirror 51. The specific size of the gap isabout 0.2 mm, for example, but should not be limited thereto. The gapmay be in any size as far as the first reflection mirror 51 does notcontact with the tip end of the first light blocking portion 81 a and asfar as the stray light which would otherwise pass through the gap can beblocked effectively.

Since the lid-like holding member 62 and the first light blockingportion 81 a are molded as a single piece, it is possible to simplifythe production process and to reduce the number of components than inthe case where the first light blocking portion 81 a is providedseparately. Further, since the first reflection mirror 51 is fixedlypositioned on the housing 61, a simple action of attaching the lid-likeholding member 62 to the housing 61 completes positioning of the endsurface of the first reflection mirror 51 with respect to the firstlight blocking portion 81 a. This structure enables a simple andhigh-precision positioning of the components.

As additional effects, the rib shape adopted by the first light blockingportion 81 a not only facilitates molding and demolding of the lid-likeholding member 62, but also enhances the mechanical strength of theengagement grooves 62 a whose shape corresponds to a part of thecolumnar side face and thereby prevents deformation of the frame.

FIG. 5 and FIG. 6 are perspective views of the scanning unit 43 in whichthe housing 61 and the lid-like holding member 62 are combined, asviewed from the platen glass 41 side. The light guiding members 71 arefitted in the engagement grooves 62 a. The slit St between the two lightguiding members 71 leads to the first reflection mirror 51 and the firstlight blocking portion 81 a. The gap between the end surface of thefirst reflection mirror 51 and the tip end of the first light blockingportion 81 a is narrow enough to block stray light, and not shownherein.

The first reflection mirror 51 is located directly below the slit St.When the reading light, emitted from the light exit planes of the lightguiding members 71 in the light source unit and reflected by an originalor an object to be illuminated, enters the inside of the housing throughthe slit St, the reading light is firstly reflected by the firstreflection mirror 51 toward the second reflection mirror 52. Similarly,stray light except the reading light reflected by the original passesthrough the slit St and firstly reaches the first reflection mirror 51.Hence, the first reflection mirror 51 is affected by stray light moreheavily than the second to fifth reflection mirrors 52-55, and requiressufficient measures against stray light.

According to the present invention as described above, the first lightblocking portion 81 a is provided face to face with the end surface ofthe first reflection mirror 51 which is arranged most closely to anoriginal (an object to be illuminated), and the length of the firstlight blocking portion 81 a is substantially equal to the length of thefirst reflection mirror 51. Accordingly, as shown in FIG. 4, the straylight 82 a passing through the slit St and reaching the end surface ofthe first reflection mirror 51 can be effectively blocked by the firstlight blocking portion 81 a. In addition, since the gap between the endsurface of the first reflection mirror 51 and the first light blockingportion 81 a is small, this structure has an effect of blocking entry ofdust into the housing through the slit St which serves as the openingand preventing deterioration of optical characteristics caused byadhesion of dust inside the housing 61.

According to the first embodiment as described above, the end surface ofthe first reflection mirror 51 is opposed to the first light blockingportion 81 a with a gap. This structure can prevent vignetting of thereading light on the reflecting surface side and can simultaneouslyprevent entry of the stray light 82 a at the end surface of the firstreflection mirror 51. Besides, even when the frame is deformed due toimpact or heat on the apparatus, this structure can limit deformation orfall of the first reflection mirror 51, and can prevent deviation of theoptical axis of the first reflection mirror 51. Accordingly, it ispossible to provide an image reading apparatus and an image formingapparatus which are capable of preventing stray light sufficiently,while preventing not only deviation of the optical axis due tointerference between the frame and the mirror but also vignetting of thereading light on the reflecting surface side of the mirror.

Second Embodiment

FIGS. 7 and 8 are cross sections of the image reading apparatus in theimage forming apparatus according to the second embodiment of thepresent invention. This embodiment provides a second light blockingportion 81 b, in addition to the first light blocking portion 81 a, onthe back side of one of the engagement grooves 62 a in the lid-likeholding member 62. The rest of the components are similar to thosementioned in the first embodiment, and detailed description thereof isomitted.

As shown in FIG. 7 and FIG. 8, the light guiding members 71 are fittedin the engagement grooves 62 a in the lid-like holding member 62. One ofthe engagement grooves 62 a is integrated with the rib-shaped firstlight blocking portion 81 a and the second light blocking portion 81 bwhich extend longitudinally along the light guiding member 71, on theback side of the groove exposed to the inside of the housing 61.

The longitudinal length of the first light blocking portion 81 a issubstantially equal to the longitudinal length of the first reflectionmirror 51. The tip end of the rib-shaped first light blocking portion 81a is opposed to an end surface of the first reflection mirror 51, with agap therebetween. These components are opposed in the vicinity of achamfered corner between the end surface and the reflecting surface.Thus, the tip end of the first light blocking portion 81 a does notcover the reflecting surface of the first reflection mirror 51, and doesnot contact with the first reflection mirror 51.

The second light blocking portion 81 b has a higher rib than the firstlight blocking portion 81 a. The second light blocking portion 81 b issituated on the back surface side of the first reflection mirror 51opposite to the reflecting surface thereof, and extends perpendicularlydownwardly, as seen in the figure, between the first reflection mirror51 and the third reflection mirror 53. The rib of the second lightblocking portion 81 b is at least high enough to obstruct an imaginarystraight line from the gap between the first reflection mirror 51 andthe first light blocking portion 81 a to the third reflection mirror 53,but not so high as to obstruct the optical path of the reading lightreflected by the third reflection mirror 53 toward the fourth reflectionmirror 54. Hence, similar to the first light blocking portion 81 a, thesecond light blocking portion 81 b does not cover the reflectingsurfaces of the first reflection mirror 51 and the third reflectionmirror 53, and does not contact with the first reflection mirror 51.

In this embodiment, the tip ends of the first light blocking portion 81a and the second light blocking portion 81 b do not cover the reflectingsurfaces of the first reflection mirror 51 and the third reflectionmirror 53, respectively. This structure does not obstruct entry of thereading light at the reflecting surfaces of the first reflection mirror51 and the third reflection mirror 53, and can prevent vignetting of thereading light.

If stray light enters the end surface of the first reflection mirror 51,the stray light that has entered from the end surface is transmittedthrough the glass of the first reflection mirror 51. As a result, straylight reflected or refracted inside the mirror is allowed to enter theinside of the housing 61. However, according to the present invention,the first light blocking portion 81 a is opposed to the first reflectionmirror 51 in the vicinity of the corner near the reflecting surface ofthe first reflection mirror 51, this structure can prevent the straylight 82 a which enters through the slit St from being incident on theend surface of the first reflection mirror 51 and from reaching the CCD47 through the inside of the housing 61. Since the length of the firstreflection mirror 51 is substantially equal to the length of the firstlight blocking portion 81 a, the above-mentioned measures against straylight can block stray light over the entire length of the firstreflection mirror 51 and can improve the effect further.

Besides, not only the tip end of the first light blocking portion 81 ais separated by a gap from, and is not in contact with, the end surfaceof the first reflection mirror 51, but also the second light blockingportion 81 b is not in contact with the first reflection mirror 51. Thisstructure addresses deformation of the frame and other accidents due toexternal impact or heat during the operation or transport of the imageforming apparatus and the image reading apparatus. In case of suchaccidents, this structure can avoid interference between the firstreflection mirror 51 and the first and second light blocking portions 81a, 81 b, and can reduce the risk of deviation of the optical axis of thefirst reflection mirror 51 due to deformation or fall of the firstreflection mirror 51. The specific size of the gap is about 0.2 mm, forexample, but should not be limited thereto. The gap may be in any sizeas far as the first reflection mirror 51 does not contact with the tipend of the first light blocking portion 81 a and as far as the straylight which would otherwise pass through the gap can be blockedeffectively.

Since the lid-like holding member 62, the first light blocking portion81 a, and the second light blocking portion 81 b are molded as a singlepiece, it is possible to simplify the production process and to reducethe number of components than in the case where the first light blockingportion 81 a and the second light blocking portion 81 b are providedseparately. Further, since the first reflection mirror 51 is fixedlypositioned on the housing 61, a simple action of attaching the lid-likeholding member 62 to the housing 61 completes not only positioning ofthe end surface of the first reflection mirror 51 with respect to thefirst light blocking portion 81 a, but also positioning of the secondlight blocking portion 81 b between the gap and the third reflectionmirror 53. This structure enables a simple and high-precisionpositioning of the components.

As additional effects, the rib shapes adopted by the first lightblocking portion 81 a and the second light blocking portion 81 b notonly facilitate molding and demolding of the lid-like holding member 62,but also enhance the mechanical strength of the engagement grooves 62 awhose shape corresponds to a part of the columnar side face and therebyprevent deformation of the frame.

The longitudinal length of the second light blocking portion 81 b may belonger or shorter than the first reflection mirror 51 and the firstlight blocking portion 81 a. This is because the first to fifthreflection mirrors 51-55 which constitute the reflective unit of theimage reading apparatus in the present invention are designed to reducetheir longitudinal lengths gradually along the optical path of thereading light. In other words, the third reflection mirror 53 is shorterthan the first reflection mirror 51. Therefore, the second lightblocking portion 81 b only needs to have a length sufficient to blockthe stray light entering the reflecting surface of the third reflectionmirror 53, and is not essentially as long as the first reflection mirror51. Nevertheless, for a sufficient blocking effect against the straylight, the second light blocking portion 81 b is preferably designed aslong as possible.

As shown in FIG. 8, the stray light 82 a transmitted through the slit Stinto the housing 61 and advancing toward the end surface of the firstreflection mirror 51 is blocked by the first light blocking portion 81a. The gap between the end surface of the first reflection mirror 51 andthe tip end of the first light blocking portion 81 a is so narrow as,for example, about 0.2 mm. Hence, light travelling at a considerableangle toward the end surface of the first reflection mirror 51 isunlikely to pass through this gap. However, if the stray light 82 badvances in a direction parallel to the end surface of the firstreflection mirror 51, the stray light 82 b passes through the gap andadvances toward the third reflection mirror 53.

In this embodiment, the second light blocking portion 81 b is integratedwith one of the engagement grooves 62 a and is located between the gapand the reflecting surface of the third reflection mirror 53. Therefore,even if the stray light 82 b may pass through the gap and may advancetoward the third reflection mirror 53, the second light blocking portion81 b can block the stray light 82 b to prevent the stray light 82 b frombeing reflected by the third reflection mirror 53 and from reaching theCCD 47.

According to the second embodiment as described above, the end surfaceof the first reflection mirror 51 is opposed to the first light blockingportion 81 a with a gap. This structure can prevent vignetting of thereading light on the reflecting surface side and can simultaneouslyprevent entry of the stray light 82 a at the end surface of the firstreflection mirror 51. Besides, even when the frame is deformed due toimpact or heat on the apparatus, this structure can limit deformation orfall of the first reflection mirror 51, and can prevent deviation of theoptical axis of the first reflection mirror 51. In addition, the secondlight blocking portion 81 b provided between the gap and the thirdreflection mirror 53 can effectively block even the stray light 82 bwhich has passed through the gap, and can further prevent the straylight from reaching the CCD 47. Accordingly, it is possible to providean image reading apparatus and an image forming apparatus which arecapable of preventing stray light sufficiently, while preventing notonly deviation of the optical axis due to interference between the frameand the mirror but also vignetting of the reading light on thereflecting surface side of the mirror.

Third Embodiment

The direction in which the second light blocking portion 81 b extends isnot limited to the perpendicularly downward direction, but may be, forexample, a direction parallel to the back surface side of the firstreflection mirror 51. Also in this case, the rib of the second lightblocking portion 81 b is at least high enough to obstruct an imaginarystraight line from the gap between the first reflection mirror 51 andthe first light blocking portion 81 a to the third reflection mirror 53,but not so high as to obstruct the optical path of the reading lightreflected by the third reflection mirror 53 toward the fourth reflectionmirror 54.

Hereinbefore, the preferred embodiments and modified examples of thepresent invention are described with reference to the attached drawings.Needless to say, however, the present invention should not be limited tothese embodiments and examples. It is apparent that a person skilled inthe art can conceive various changes and modifications within the scoperecited in the claims. Such changes and modifications are naturallyunderstood to be within the technological scope of the presentinvention.

DESCRIPTION OF THE REFERENCE NUMERALS

-   1 image forming apparatus-   2 image reading apparatus-   3 original transporting apparatus-   4 printing unit-   5 feeding cassette-   11 optical scanning device-   12 development device-   13 photosensitive drum-   14 drum cleaning device-   15 charging unit-   17 fixing device-   21 intermediate transfer belt-   26 secondary transfer device-   43 scanning unit-   46 imaging lens-   47 CCD (reading unit)-   51-55 first to fifth reflection mirrors-   61 housing-   62 lid-like holding member (holding member)-   62 a engagement grooves-   63 CCD board-   64 LED board (substrate)-   71 light guiding member-   72 LED (light emitting element)-   81 a first light blocking portion-   81 b second light blocking portion-   82 a, 82 b stray light-   St slit

What is claimed is:
 1. An image reading apparatus comprising: a scannerincorporating: a light source unit for illuminating an object to beilluminated; a reading unit for reading the object illuminated by thelight source unit; and a plurality of reflection mirrors forsequentially reflecting reading light reflected by the object toward thereading unit; and a guide that enables the scanner to move with respectto the object, wherein a first reflection mirror that first reflects thereading light, among the plurality of reflection mirrors, is arrangednear a slit provided to guide the reading light into the scanner, thefirst reflection mirror partially blocking the slit.
 2. The imagereading apparatus according to claim 1, wherein the plurality ofreflection mirrors comprise a second reflection mirror that reflects thereading light reflected by the first reflection mirror, and the secondreflection mirror is arranged farther than the first reflection mirrorfrom the object.
 3. The image reading apparatus according to claim 1,wherein the plurality of reflection mirrors, in the scanner, comprise afinal reflection mirror that is arranged upstream or downstream in amovement direction of the scanner and finally reflects the readinglight, and a pre-final reflection mirror that is arranged before thefinal reflection mirror and reflects the reading light toward the finalreflection mirror, and the final reflection mirror and the pre-finalreflection mirror are arranged to face each other in the movementdirection of the scanner.
 4. The image reading apparatus according toclaim 1, wherein the plurality of reflection mirrors are arranged toface each other in a movement direction of the scanner, and at least twoof optical paths of the reading light reflected by the plurality ofreflection mirrors intersect each other.
 5. An image forming apparatuscomprising: the image reading apparatus according to claim
 1. 6. Animage reading apparatus comprising: a scanner incorporating: a lightsource unit for illuminating an object to be illuminated; a reading unitfor reading the object illuminated by the light source unit; and aplurality of reflection mirrors for sequentially reflecting readinglight reflected by the object toward the reading unit; and at least onepair of rollers that move the object with respect to the scanner,wherein a first reflection mirror that first reflects the reading light,among the plurality of reflection mirrors, is arranged near a slitprovided to guide the reading light into the scanner, the firstreflection mirror partially blocking the slit.
 7. The image readingapparatus according to claim 6, wherein the plurality of reflectionmirrors comprise a second reflection mirror that reflects the readinglight reflected by the first reflection mirror, and the secondreflection mirror is arranged farther than the first reflection mirrorfrom the object.
 8. The image reading apparatus according to claim 6,wherein the plurality of reflection mirrors, in the scanner, comprise afinal reflection mirror that is arranged upstream or downstream in amovement direction of the scanner and finally reflects the readinglight, and a pre-final reflection mirror that is arranged before thefinal reflection mirror and reflects the reading light toward the finalreflection mirror, and the final reflection mirror and the pre-finalreflection mirror are arranged to face each other in the movementdirection of the scanner.
 9. The image reading apparatus according toclaim 6, wherein the plurality of reflection mirrors are arranged toface each other in a movement direction of the scanner, and at least twoof optical paths of the reading light reflected by the plurality ofreflection mirrors intersect each other.
 10. An image forming apparatuscomprising: the image reading apparatus according to claim
 6. 11. Animage reading apparatus comprising: a scanner incorporating: a lightsource unit for illuminating an object to be illuminated; a reading unitfor reading the object illuminated by the light source unit; and aplurality of reflection mirrors for sequentially reflecting readinglight reflected by the object toward the reading unit; and a scanningmechanism that moves the scanner relatively with respect to the object,wherein a first reflection mirror that first reflects the reading light,among the plurality of reflection mirrors, is arranged near a slitprovided to guide the reading light into the scanner, the firstreflection mirror partially blocking the slit.
 12. The image readingapparatus according to claim 11, wherein the plurality of reflectionmirrors comprise a second reflection mirror that reflects the readinglight reflected by the first reflection mirror, and the secondreflection mirror is arranged farther than the first reflection mirrorfrom the object.
 13. The image reading apparatus according to claim 11,wherein the plurality of reflection mirrors, in the scanner, comprise afinal reflection mirror that is arranged upstream or downstream in amovement direction of the scanner and finally reflects the readinglight, and a pre-final reflection mirror that is arranged before thefinal reflection mirror and reflects the reading light toward the finalreflection mirror, and the final reflection mirror and the pre-finalreflection mirror are arranged to face each other in the movementdirection of the scanner.
 14. The image reading apparatus according toclaim 11, wherein the plurality of reflection mirrors are arranged toface each other in a movement direction of the scanner, and at least twoof optical paths of the reading light reflected by the plurality ofreflection mirrors intersect each other.
 15. An image forming apparatuscomprising: the image reading apparatus according to claim 11.